I. Field of the Invention
The present invention relates to an apparatus for the attachment of a shaft, particularly that of a rotating control device, to an operating unit or actuator drive system. More particularly, the invention concerns a device of the class that includes a centering shaft adapter in which separate mechanisms are used to (1) accommodate shafts of varying sizes while keeping any shaft concentric with the hub of a rotating actuator or drive system attached to the adapter and to (2) generate the clamping force required to transfer the torque load between the shaft and the adapter.
II. Related Art
Many control devices include motors driving rotating hubs usually having meshing splines of a given pitch which, in turn, are used to operate a concentrically aligned rotary axle or shaft of a control device such as a butterfly ventilating valve, damper, or the like. An integral adapter device is used to directly couple the rotating output hub to an input shaft of a control device in concentric arrangement. The drive units are designed to be used with a variety of input or control device shaft sizes. However, generally in the past, it has been necessary to provide special arrangements in order to change shaft sizes. For example, a series of adapters might be used to accommodate shafts of different sizes to enable the system to maintain the desired concentric arrangement. Alternatively, a plurality of separate inserts have been devised, one for each size shaft to space the shaft from the clamp jaws the appropriate amount to maintain a concentricity with the output hub of the actuator.
Mechanical clamping devices also exist which adjust the center of the clamped shaft to maintain concentricity with a corresponding hub over a range of shaft sizes. One such device is illustrated and described in U.S. Pat. No. 5,544,970 to Studer which utilizes a hollow member having internal and external threads which cooperate to open and close upper and lower jaw members to clamp about a shaft of interest. The outer threads engage an outer housing member which, in turn, operates the lower jaw; whereas the inner threads engage a bolt that pulls on the upper jaw. A thread pitch ratio between the inner and outer threads is used to move the jaws an unequal amount so that the center between the jaws remains concentric with the axis of the hub. Although this successfully accomplishes the desired adjustment, the design has several drawbacks or limitations. First, the centering mechanism must also supply the clamping force so that it must be built to transmit the entire system torque; and second, the double-threaded member is difficult to produce and involves the utilization of a very fine pitch on the outside thread which is readily susceptible to clogging and cross threading.
Thus, there remains a definite need in the art for an adaptive coupling mechanism that utilizes parts that are readily made and provides a separate mechanism for the clamping and centering functions and which can accommodate a wide range of shaft sizes.
The present invention provides a single, relatively simple mechanism for concentrically adapting the output hub of a direct coupled actuator to operate control device shafts of varying sizes, thereby obviating the need for separate connecting devices or inserts to accommodate a range of shaft sizes. In this manner, a direct coupled actuator can be mounted on shafts of different sizes interchangeably while maintaining concentric alignment between the output hub of the actuator and the shaft of interest. In addition to being a self-centering shaft adapter, the adapter of the invention utilizes separate mechanisms to keep the shaft and output hub concentric and to generate the clamping force required to transfer the torque load from the shaft to the adapter. In this manner, the self-centering mechanism is not required to transmit the full torque load between the adapter and the clamped shaft but only to keep the shaft and output hub concentric. The system consists of opposed jaws that grip each side of the shaft and are mechanically linked to insure that both jaws travel in equal amounts with respect to the geometric center of an integral drive hub when adjusted to accommodate a shaft that is being clamped.
The mechanism may take any of several forms including double and single rack and pinion systems, beam systems, and cam and follower devices. Each of these mechanisms operates to concentrically open and close a pair of clamping jaws about a geometric center using a mechanical linkage operated by a conventional threaded fastening arrangement, as will be described.